The objective is to define the relationship between diversity of structure in MHC genes and the function of those genes in the immune system. The significance of these studies stems from the fact that our understanding of the role of MHC genes in immune function is largely derived from analyses based on polymorphisms defined in inbred mice. Since these structurally relevant polymorphisms influence function of the MHC products, it is of great interest to define which polymorphisms are relevant to the diversification of alleles within inbreeding populations and which are representative of individuals from genetically isolated populations. The specific aims are: 1) To characterize a unique MHC haplotype by comparison with two other previously described haplotypes defining features of haplotype variation that are relevant to MHC function and evolution. 2) To determine if haplotypes other than H-2b undergo copy event that lead to diversification of genes encoding antigen presenting products of the class I and class II regions of the H-2 complex. 3) To define the relative contributions of spontaneous point mutations and copy mediated mutations in the diversification and polymorphism of MHC genes. 4) To analyze the contribution of polymorphic sequences to encoded function. The analyses will be accomplished by the molecular genetic comparison of cloned genes among genetically defined mouse strains. Cosmid and phage genomic libraries of A.CA, B10.M, C57BL/6 and C57BL/10 lines will be analyzed to isolate homologous class I and class II sequences. Comparative studies will be based on restriction endonuclease mapping and DNA sequence analyses of genes derived from each library. Synthetic oligonucleotide probes will be used to identify specific DNA sequences that are shared by MHC genes within and among the H-2f and H-2b haplotypes. Direct DNA sequence analysis of homologous portions of MHC genes will provide estimates of spontaneous mutation and copy mediated mutation rates. Hybrid genes will be constructed and introduced into cells in culture to assess function.